TP-PCR combined with long-read sequencing for screening of fragile X syndrome carriers
Chen Yujiao1, Li Shanshan1, Zhang Meng1
1Prenatal Diagnostic Center, Beijing Obstetrics and Gynecology Hospital, Beijing Maternal and Child Health Care Hospital, Capital Medical University, Beijing, 100026, China.
Background:
To accurately screen Fragile X syndrome (FXS) carriers during pregnancy, number of CGG repeats for full mutation (FM), low-proportion mosaicism, the presence of AGG interruptions, and microdeletions were identified.
Methods:
Long-read sequencing (LRS) was developed and evaluated premutation (PM) by comparing to triplet repeat-primed PCR (TP-PCR). In the follow-up, pregnancy outcomes in carrying FMR1 expanded alleles and the screening of their newborn offspring were inquired.
Results:
The results showed that LRS could accurately detect CGG repeats in clinical samples (blood and amniotic fluid samples) with premutation (PM). Furthermore, LRS could directly determine that mosaicism in FXS (29/48/77 repeats), offering a mosaicism ratio of 3%. The results of CGG repeats of FMR1 by LRS demonstrated that a history of infertility had PM alleles (29/71 repeats). In addition, LRS demonstrated a 71 bp deletion exon 1 of FMR1 in carrying PM, whereas CGG repeats was lower than 0 via detecting by TP-PCR.
Conclusion:
Our study provides the first evidence of low-proportion mosaicism and microdeletion via LRS method, which may prove to be an option for the additional cases of FXS during pregnancy.
